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​Nearby relief

  A. Question

  1. Is there nearby thermal relief in a stream where trout can go as a summer day heats up?

  2. In particular, can colder temperature be expected where the water is deeper, has faster flow, or is shaded?

  3. Results of limited testing are shown in the plot below and described in the text that follows.

    Nearby | Movement | Signal

No temperature differences at main-stem riffles and cutbank


  B. Testing

  1. Two sensors were installed in the main stem at 9079 ft at unshaded riffles and at a nearby shaded cutbank.

  2. The cutbank sensor was 14 inches deeper, at the river bottom.

  3. Water temperatures were measured continuously at 30-minute intervals over 49 days in July-August 2017.

  4. Water temperatures at the riffles and at the cutbank were found to be the same.

  5. This is shown in the plot below.

  6. Also, using a hand-held sensor, temperatures were measured where depth, flow , and shading differed.

  7. This was conducted at Priest, Tenderfoot, and Ryman.

  8. Measurements were roughly 200-400 yards upstream from the tributary's outfall at the main stem.

  9. The measurement section at each tributary was approximately 100 ft in length.

  10. Stream depths were 4-18 inches in those sections.

  11. Measurements were made on August 29 and 31, 2018.

  C. Conclusion​

  1. Water temperatures were found to be the same across the variety of conditions in the test sections.

  2. Based on this limited investigation, it appears that no nearby thermal relief is available for trout.

  3. The water likely is too well mixed for localized colder temperatures to occur.

  4. If there is colder water further away, such as upstream, will trout move to it temporarily for relief?

    Nearby| Movement | Signal

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